1. Field of the Invention
The present invention relates to a control apparatus for an internal combustion engine including a fuel injection mechanism (in-cylinder injector) injecting fuel at high pressure into a cylinder, or an internal combustion engine including, in addition to the aforementioned fuel injection mechanism, another type of fuel injection mechanism (intake manifold injector) injecting fuel towards an intake manifold or intake port. Particularly, the present invention relates to control of an internal combustion engine in an idling mode.
2. Description of the Background Art
There is known an engine including a first fuel injection valve (in-cylinder injector) for injecting fuel into the combustion chamber of a gasoline engine and a second fuel injection valve (intake manifold injector) to inject fuel into an intake manifold, wherein the in-cylinder injector and the intake manifold injector partake in fuel injection according to the engine speed and internal combustion engine load. There is also known a direct injection engine including only a fuel injection valve (in-cylinder injector) to inject fuel into the combustion chamber of the gasoline engine. In a high-pressure fuel system including an in-cylinder injector, fuel having pressure increased by a high-pressure fuel pump is supplied to the in-cylinder injector via a delivery pipe, whereby the in-cylinder injector injects high-pressure fuel into the combustion chamber of each cylinder in the internal combustion engine.
Further, there is also known a diesel engine with a common rail type fuel injection system. In the common rail type fuel injection system, fuel having pressure increased by a high-pressure fuel pump is stored at the common rail. High-pressure fuel is injected into the combustion chamber of each cylinder in the diesel engine from the common rail by opening/closing an electromagnetic valve.
For the purpose of generating such high-pressure fuel, a high-pressure fuel pump that drives a cylinder through a cam provided at a drive shaft coupled to a crankshaft of the internal combustion engine is employed. The high-pressure fuel pump includes a pump plunger that reciprocates in a cylinder by the rotation of the cam, and a pressurizing chamber formed of the cylinder and pump plunger. To this pressurizing chamber are connected a pump supply pipe communicating with a feed pump that feeds fuel from a fuel tank, a return pipe to return the fuel flowing out from the pressurizing chamber into the fuel tank, and a high-pressure delivery pipe to deliver the fuel in the pressurizing chamber towards the in-cylinder injector. The high-pressure fuel pump is provided with an electromagnetic spill valve for opening/closing the pump supply pipe and high-pressure delivery pipe with respect to the pressurizing chamber.
When the electromagnetic spill valve is open and the pump plunger moves in the direction of increasing the volume of the pressurizing chamber, i.e. when the high-pressure fuel pump is in an intake stroke, fuel is drawn from the pump supply pipe into the pressurizing chamber. When the pump plunger moves in the direction of reducing the volume of the pressurizing chamber, i.e. when the high-pressure fuel pump is in a delivery stroke, and the electromagnetic spill valve is closed, the pump supply pipe and return pipe are cut from the pressurizing chamber, and the fuel in the pressurizing chamber is delivered to the in-cylinder injector via the high-pressure delivery pipe.
Since fuel is delivered towards the in-cylinder injector only during the period where the electromagnetic spill valve is closed in the delivery stroke in accordance with the high-pressure fuel pump, the amount of fuel pumped out can be adjusted by controlling the time to start closing the electromagnetic spill valve (adjusting the closing period of the electromagnetic spill valve). Specifically, the amount of fuel pumped out is increased by setting the time to start closing the electromagnetic spill valve earlier to increase the valve-closing period. The amount of fuel pumped out can be reduced by retarding the time to start closing the electromagnetic spill valve to shorten the valve-closing period.
By applying pressure to the fuel output from the feed pump with the high-pressure fuel pump and delivering the pressurized fuel towards the in-cylinder injector, fuel injection can be effected appropriately even for an internal combustion engine that injects fuel directly into the combustion chamber.
When the electromagnetic spill valve is to be closed in the delivery stroke of the high-pressure fuel pump, the fuel will flow, not only towards the high-pressure delivery pipe, but also towards the return pipe since the volume of the pressurizing chamber is currently reduced. If the electromagnetic spill valve is to be closed under such a state, the force by the fuel that will flow as set forth above is urged in the closing-valve operation, increasing the impact force when the electromagnetic spill valve is closed. Reflecting this increase in impact, the operation noise of the electromagnetic spill valve (the noise of the closing valve) will also become larger. This operation noise of the electromagnetic spill valve will occur continuously every time the electromagnetic spill valve is closed.
During a normal operation mode of the internal combustion engine, the continuous operation noise caused by every closing of the electromagnetic spill valve is not so disturbing since the operation noise of the internal combustion engine such as the combustion noise of the air-fuel mixture is relatively large. However, when the operation noise of the internal combustion engine per se is small such as in an idling mode of the internal combustion engine, the continuous operation noise of the electromagnetic spill valve will become so audible that the disturbance thereof can no longer be neglected.
Japanese Patent Laying-Open No. 2001-41088 discloses a fuel pump control device that can have the continuous operation noise caused at every closing of the electromagnetic spill valve reduced. The control device disclosed in this publication includes a fuel pump that draws in fuel into the pressurizing chamber and delivers the fuel towards the fuel injection valve of the internal combustion engine by altering the volume of the pressurizing chamber based on the relative movement between the cylinder and pump plunger caused by the rotation of the cam, and a spill valve for opening/closing the communication between the pressurizing chamber and the spill channel from which the fuel flows out from the pressurizing chamber. The amount of fuel pumped out towards the fuel injection valve from the fuel pump is adjusted by controlling the spill valve closing period. By controlling the spill valve based on the operation state of the internal combustion engine, the number of times of pumping out fuel by the fuel pump during a predetermined period of time can be adjusted to alter the number of times of fuel injection through the fuel injection valve per one fuel delivery. The control device includes a control unit reducing the number of times of fuel injection per one fuel delivery in a low engine load mode.
In accordance with this fuel pump control device, the required amount of fuel delivered at one time is reduced since the number of times of fuel injection per one fuel delivery is reduced in a low engine load mode where the continuous operation noise of the electromagnetic spill valve becomes relatively large. Accordingly, the time to start closing the electromagnetic spill valve can be set at a time further closer to top dead center. The cam rate indicating the relative movement between the pump plunger and the cylinder becomes smaller as a function of approaching the top dead center. Accordingly, the cam rate at the time of closing the electromagnetic spill valve can be reduced to further lower the closing noise of the electromagnetic spill valve. By lowering the closing noise of the electromagnetic spill valve, the continuous operation noise cause at every closing operation of the electromagnetic spill valve can be reduced.
Although the control device disclosed in the aforementioned publication is advantageous in that the operation noise is reduced, the operation noise will still occur when the electromagnetic spill valve of the high-pressure fuel pump closes since the high-pressure fuel pump is not stopped (i.e., the electromagnetic spill valve is continuously open) in a low engine load mode. Further, the fuel injection quantity is low such that combustion is apt to become unstable in an idle region (particularly, in an idle region at the low speed and low load side). If fuel injection from the in-cylinder injector is stopped in an idle region, deposits may accumulate at the injection hole of the in-cylinder injector.